1. Field of the Invention
The present invention relates to a capping mechanism for an ink jet head applicable to a method and an apparatus for ink jet recording of a scanning type, a full-line type, or others which utilize ink jet recording, and to an ink jet apparatus equipped with such a mechanism. The present invention is applicable to various apparatuses having a function to record on a transparent recording medium such as paper, cloth, or sheet and others for OHP use in a liquid ink or ink in a state that a solid ink is liquefied (hereinafter referred to simply as ink).
2. Related Background Art
In recent years, there have been on the market as ink jet recording apparatuses, monochromatic ink jet recording apparatuses capable of recording only in a single color, and those capable of recording in colors. In these ink jet recording apparatuses, a capping mechanism is provided for an ink jet recording head which may be left intact for a long period of time. Usually, a cap made of a resilient rubber material is arranged to be in contact with the head surface (the surface of orifices) under pressure to make an enclosed space for the head surface, which is shut from the atmosphere, thus preventing the orifices (discharge ports) from being clogged due to drying of ink.
There are also in practical use the ink Jet recording apparatuses having an ink suction device and ink compression device together with a head recovery function in order to maintain among others the stabilized discharge of ink jet head or improve the defective discharging condition thereof by utilization of the capping mechanism. The typical structure of a recovery apparatus having a suction device is shown in FIG. 34 and FIG. 35, for example. As shown in these figures, a resilient cap 228 is arranged to advance to or retract from the recording head 232 of a scanning type when the head is in the home position. There are provided a capping mechanism which allows the cap 228 to abut on the recording head when it advances, and keep the space formed by the cap 228 and the recording head 232 in a state of being shut from the atmosphere, and a source 229 for manually generating a negative pressure, which is connected to this cap 228 through a tube 230 serving as a connecting member. Also, a pumping mechanism is provided for sucking ink from the recording head 232 by actuating the source 229 for manually generating negative pressure through the cap 228 which is in contact closely with the recording head under pressure, as well as for sucking ink from the interior of the cap by actuating the source 229 for manually generating negative pressure through the cap 228 when the cap is in a state of being released to the atmosphere. In this respect, it is needless to mention that the source 229 for manually generating negative pressure can be arranged as a source of an automatic type for generating negative pressure.
Here, the recording head 232 is kept airtight by the capping which is provided by the cap 228 while the recording head disengages from printing. Thus the discharge ports of the recording head can be prevented from being dried, and also, from adhesion of dust particles and others in the air outside. In this way, the stabilized discharge is executable. Meanwhile, however, the usual discharge may become inexecutable, that is, a case where a defective ink discharge may ensue, due to some causes, such as the generation of bubbles in the ink passages in the interior of the recording head, adhesion of dust particles to the ink discharge ports, or the ink which becomes overly viscous. Therefore, in order to recover the discharge capability of the recording head for the execution of the stabilized discharge, the above-mentioned pumping mechanism is actuated while the recording head 232 is capped by the cap 228 so that the head is in the airtight condition, and then, ink is sucked from the ink discharge ports of the recording head.
On the other hand, fine liquid particles such as ink mist, which are generated at the time of ink discharging, adhere to the surface of the recording head (orifice surface). This may also disturb the usual ink discharge in some cases. Therefore, after the completion of a given recording, a cleaning blade is used for a contact cleaning of the surface of the recording head. In either case described above, the conventional capping mechanism and cleaning mechanism are of the type that directly works on the ink jet recording head.
While these conventional capping and cleaning mechanisms are recognized to be effective in attaining the stabilized discharge of the recording head 232 in a long-term view, the inventor hereof has come to notice a problem yet to be solved in this respect. In other words, no one has given any attention to the condition of the surface of the cap on the recording head side at all, but the inventor hereof has found that firmly fixed ink, dust particles, paper fluffs, and others are accumulated on the surface of the cap on the recording head side, and that such accumulation, if exists, leads to an imperfect airtightness provided by the cap 228 for the recording head. Thus the capping effect is not good enough for the head which is on standby, causing the discharge ports to be dried, and also, creating the overly viscous ink. The discharging condition of the recording head becomes unstable inevitably or it requires more time to recover the recording head, thus wastefully using more ink for its recovery. This state is represented in FIG. 34 and FIG. 35. Here, with reference to FIG. 34 and FIG. 35, the description will be made of the present invention in detail with a view to solving the new problem thus found.
As shown in FIG. 34, if dust particles and paper fluffs 231 adhere to the portion where the cap 228 abuts on the recording head 232 (the surface of the cap on the recording head side), a space 233 is created in the vicinity of the inclusion 231 such as dust particles or paper fluffs existing between the cap 228 and recording head 232. As a result, the airtightness to be maintained between the cap 228 and recording head 232 cannot be obtained by capping, thus making it impossible to prevent the recording head from being dried. Also, it becomes impossible to carry out a sufficient suction for the recovery of the recording head or avoid ink leakage when exerting compression to recover the recording head. Consequently, in some cases, the surface of the recording head is more stained instead of being cleaned. Particularly, in executing the suction recovery, although the suction can be made to a certain extent immediately after the actuation of sucking, but the air outside is also sucked in when the suction is continued. Therefore, in some cases, the condition is forced to change so much as to make the suction from the interior of the recording head inexecutable at all. In order to improve this situation, it is attempted to increase the number of cleaning operations, with the result that no essential effects are produced on improvement.
To solve the new problem by the present invention will not only result in a more reliable capping for the recording head, but also result in the elimination of the wasteful use of time and ink for the recovery required. Therefore, the solution of this problem is extremely significant in view of the provision of a more reliable ink jet technique. Further, the present invention contributes to obtaining a more stability in the ink discharge of an ink jet recording head. It is also an object of the present invention to provide a more rationalized capping structure with a view to solving the drawback of the cap as described above.
The technical aspect of the present invention is equally applicable to the cap to be used for an ink jet head of a full-line type. Here, since a cap which is integrally formed by a plurality of capping units for a head unit having two to four ink jet heads tends to create uneven distribution of pressure to the head surface than those caps which are individually arranged to operate for such a head unit, the possibility is that each of the heads is more easily affected by the above-mentioned problem. From this point of view, the solution of the problem becomes more important.
Now, in a case of a monochromatic ink jet recording apparatus, black ink is most often used as an ink color for recording. Red, Green, and Blue are also used as required. However, since the structure is such that only one cartridge can be mounted on the carriage, a cartridge for black ink is mounted for recording in black, and if a recording is to be made in red, another cartridge for red ink should be mounted after the cartridge for black ink is removed from the carriage. Also, since only one cartridge is mountable on the carriage, only one cap is provided.
On the other hand, in a case of a full-color ink jet recording apparatus, four cartridge each for yellow, cyan, magenta, and black are usually mounted on a carriage, and caps are also arranged for each of the colors. For each of the recording heads, its discharge surface is airtightly closed by each capping, and then, should any defective discharge take place, ink is sucked from the discharge ports through the cap. In order to suck ink from each of the recording heads, it is necessary to connect each cap with the pumping mechanism per color. The resultant structure becomes inevitably complicated. Therefore, a structure is proposed, wherein the capping is carried out by only one head for all the recording heads. In this case, if a desired color ink must be sucked from the corresponding head, the carriage should be moved so that the target recording head is positioned in front of the cap for suction because there is only one cap arranged. As a result, if the recording heads are four, the positions for the carriage to suck ink should also be four. Also, there is proposed a structure wherein, besides a cap for sucking ink from the discharge ports, protective caps are arranged for each of the recording heads, which do not suck ink from them but just cover them closely.
Also, irrespective of a monochrome or full colors, a wiper is often provided for the recovery unit in order to remove foreign particles adhering to the recording head and cap. Further, the discharge port surface of a recording head is capped to maintain the airtightness when the recording head disengages from recording, hence implementing the stabilized discharge by preventing the discharge ports from being dried and also, from the adhesion of any foreign particles.
Nevertheless, in the conventional ink jet recording apparatuses described above, only one suction cap is arranged for heads for recording in plural colors. Therefore, a problem is encountered in that if a recording head for red ink is used after having used a recording head for black ink, for example, the recording in red becomes blackish due to the mixture of the black ink.
More specifically, when the recording head for black ink is being used, the discharge port surface of the recording head, that is, the surface to be capped is stained with black ink due to the ink suction, the ink wiping operation by wiper, and the flight of ink when ink is discharged from the discharge ports. In such a state, the recording head is again capped when it disengages from recording in order to prevent the discharge ports from being dried, and also, from the adhesion of any foreign particles thereto. As a result, black ink adheres to the surface of the cap which abuts on the discharge port surface (hereinafter, this surface of the cap is referred to as "sealing surface").
Subsequently, if, for example, the recording head for black ink is replaced with the recording head for red ink for recording, the black ink which has adhered to the sealing surface of the cap adheres to the discharge port surface of the recording head for red ink. When a wiping is performed in this state in order to remove foreign particles, the black ink adhering to the discharge port surface of the recording head for red ink is pressed into the interior of the discharge ports thereof. As a result, red ink and black ink are mixed. Also, even if no wiping is performed, the possibility is that the black ink adhering to the discharge port surface flows into the discharge ports at the time of recording or capping.
Here, regarding the color mixing due to the ink of different color which is pressed into the discharge ports by wiping operation, it is possible to prevent the mixed ink from being discharged by conducting a predischarge onto a place other than the recording area, the interior of the cap, for example, immediately after the wiping operation. However, when the ink adhering to the discharge port surface flows into the discharge ports to create a color mixing, it is extremely difficult to prevent it from taking place because the timing of the ink flowing into it can hardly be specified.